The invention relates in general to polymer composites and more particularly to hydrophilic-hydrophobic polymer composites. The hydrophilic-hydrophobic polymer composites may be prepared using a concentrated emulsion pathway. A polymer composite is a dispersion of particles of one kind of polymer in a continuous phase of another polymer. A Hydrophilic-hydrophobic polymer composite is a polymer composite in which one of the phases is hydrophobic and the other phase is hydrophilic. Polymer composites are of practical importance because their two phase structure often allows for a synergistic behavior regarding their mechanical properties and also for selective permeability to fluids.
Polymers which have a hydrophobic component and a hydrophilic component are known. One method which may be utilized to make hydrophilic-hydrophobic polymers is copolymerization. The copolymers produced include graft copolymers and block copolymers. However, copolymerization results in the formation of polymers which at the molecular level have a hydrophobic and hydrophilic component.
Another method for making hydrophilic-hydrophobic polymer structures is the Interpenetrating Network method. The Interpenetrating Network method is a complex two stage polymerization in which a cross-linked polymer is swelled with a second monomer and with crosslinking and activating agents, and finally subjected to a second polymerization which usually causes the formation of graft copolymers. This method, as its name implies, generally results in interpenetrating networks of two polymers, neither one of which would usually be considered a dispersed phase.
Hydrophilic-hydrophobic polymer composites may be prepared by blending. Blending involves the mixing of two polymers while they are in solution or in a molten, fluid state and often results in the formation of a nonuniform material. This method is especially unsuitable when the desired volume fraction of the dispersed phase is significantly greater than the volume fraction of the continuous phase.
Emulsion polymerization is a process which has been used to make copolymers and homopolymers. Copolymers are formed from at least two different monomers and homopolymers are polymers formed from a single monomer. In conventional emulsion polymerization, monomer droplets are dispersed in an aqueous phase containing micellar aggregates of surfactant. Micellar aggregates as used herein are colloidal particles formed by the reversible aggregation of dissolved molecules. The dispersed phase represents a relatively small volume fraction of the system and the micellar aggregates constitute the sites of the polymerization process. Another method of producing polymers is the concentrated emulsion polymerization method. This method is disclosed in the article, Polymerization in Gel-Like Emulsions, Eli Ruckenstein and Kyu-Jun Kim, Journal of Applied Polymer Science, Vol. 36, 907-923 (1988), the disclosure of which is incorporated by reference herein.
In contrast to conventional emulsion polymerization, in the concentrated emulsion case the volume fraction of the dispersed phase is very high and can be as high a 0.995. The concentrated emulsion has the appearance of a gel and the structure is similar to that of foams. In other words, the dispersed phase consists of polyhedral cells separated by a network of thin liquid films of the continuous phase. The repulsive forces between the surfactant molecules adsorbed on the surfaces of the neighboring cells are responsible for the stability of the gel. In contrast to conventional emulsion polymerization (where the polymerization takes place in the micellar aggregates), the polymerization in a concentrated emulsion takes place in the dispersed phase (which contains the initiator which was introduced before the preparation of the gel). This concentrated emulsion procedure has also been used to produce copolymers.
A useful application of polymers is in the preparation of membranes for various separation processes. However, few polymer blends were developed as permselective membranes, i.e. membranes which allow only some of the liquid components to permeate through the membrane. This is due in part to the generally low compatibility between different polymers which frequently results in nonhomogeneous structures.
One method of preparing permselective membranes is by solvent casting. Solvent casting is a procedure which includes dissolving 2 polymers in a solvent, then evaporating the solvent. However, it is not easy to identify two polymers which are mutually compatible, as a result, the membranes which are obtained by casting also may not be homogeneous. The polymers are particularly incompatible when one of the polymers is very hydrophobic and the other is very hydrophilic. To obtain good permselectivity, it is important that one of the polymers is hydrophobic and the other hydrophilic.
Therefore there still exists a need for a new simple method to produce hydrophobic-hydrophilic composites which will have a uniform structure and may have a wide variety of applications including but not limited to use as a permselective membrane.